Clinical and laboratory studies are conducted to determine etiology (infection, immunity and/or genetics) for chronic diseases of the peripheral and central nervous system. Current studies include amyotrophic lateral sclerosis, (ALS), polymyositis/dermatomyositis, demyelinating polyneuropathies and chronic Guillain-Barre syndrome, Reye's syndrome, multiple sclerosis, progressive multifocal leukoencephalopathy, subacute sclerosing panencephalitis and myasthenia gravis. Combined clinical data, genetic information, HLA and MLC typing virus serology and virus isolation studies are obtained for these studies. The nature of oligoclonal bands found in the CSF of patients with chronic neurological diseases is under investigation. A new neuromuscular disease that occurs in patients who have had poliomyelitis at an early age has been clinically defined; the possibility that this might be due to a late or slow polio virus infection or an immune reaction to it is under investigation. Abnormal immunoregulation has been recognized in patients with paraproteinemic polyneuropathies. In patients with hereditary neuropathy and elevated IgA, abnormal phenotypic markers on B lymphocytes and IgA immune complexes have been identified.